AP Chemistry Flashcards: Henderson-Hasselbalch Equation
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
What does the term [A−]/[HA] represent in the Henderson-Hasselbalch equation?
It represents the concentration ratio of the conjugate base ([A−]) to the conjugate acid ([HA]) within the buffer solution.
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What does the term [A−]/[HA] represent in the Henderson-Hasselbalch equation?
It represents the concentration ratio of the conjugate base ([A−]) to the conjugate acid ([HA]) within the buffer solution.
Based on the provided text, what is a key characteristic of a buffer solution's composition and function?
A buffer solution is made from a conjugate acid-base pair, and its key function is that its pH does not significantly change when small amounts of acid or base are added.
What two factors determine the pH of a buffer solution according to the Henderson-Hasselbalch equation?
The pH of a buffer is determined by the pKa of the weak acid and the concentration ratio of the conjugate acid-base pair ([A−]/[HA]).
What is the primary purpose of the Henderson-Hasselbalch equation?
Its primary purpose is to identify the pH of a buffer solution based on the pKa and the concentrations of the conjugate acid-base pair used to create the buffer.
State the Henderson-Hasselbalch equation.
The Henderson-Hasselbalch equation is pH = pKa + log([A−]/[HA]), which relates a buffer's pH to the pKa and the concentration ratio of the conjugate acid-base pair.
What is the effect on a buffer's pH when a small amount of acid or base is added?
Adding small amounts of acid or base does not significantly change the concentration ratio of the conjugate pair, and therefore does not significantly change the pH.
Why does the pH of a buffer resist significant change?
The pH resists change because the concentration ratio of the conjugate acid-base pair ([A−]/[HA]) does not change significantly upon addition of small amounts of acid or base.
How does the identity of the conjugate acid-base pair influence the pH of a buffer?
The identity of the pair determines the pKa value, which is a fundamental component used in the Henderson-Hasselbalch equation to calculate the buffer's pH.
If the concentration of the conjugate base [A−] is greater than the conjugate acid [HA], will the buffer's pH be greater or less than the pKa?
The pH will be greater than the pKa because the ratio [A−]/[HA] will be greater than 1, making the log term in the equation positive.
Under what condition is the pH of a buffer solution equal to the pKa of the weak acid?
The pH of a buffer equals the pKa when the concentrations of the conjugate acid and base are equal, making the ratio [A−]/[HA] equal to 1.